1. Field of the Invention
The present invention relates to a novel method of manufacturing actuators, e.g., artificial muscles, and novel applications of the actuators manufactured according to the novel method. More particularly, the invention relates to a novel chemical/mechanical/electrical treatment of membranes, e.g. ion-exchange membranes, to convert them to artificial muscles capable of undergoing electrically-controllable large deformations resembling the behavior of biological muscles. The invention further relates to a number of novel techniques for packaging and application of the said artificial muscles.
2. Background Art
The creation of controllable actuators, or synthetic muscles, is known. Artificial muscles or actuators made from ion-exchange membranes are relatively new but also known.
U.S. Pat. No. 4,522,698, to Maget, discloses a prime mover that uses pressure increases and decreases induced by converting molecules of electrochemically active material to ions, transporting ions through an electrolytic membrane and reconverting the ions to molecules. The prime mover includes gas-tight compartments filled with an electrochemically active material and separated by an electrolytic membrane, such as an ion-exchange membrane, that incorporates electrodes so that a voltage gradient can be established across the membrane to induce current flow through the membrane. When the current flows through the membrane, molecules travel through the membrane and are reconverted to molecules in the opposite compartment causing a pressure increase in the receiving compartment and a pressure decrease in the other compartment. The pressure changes are converted to mechanical motion which can be used as a driver for a mechanical load. The disadvantages of this technique are that the resulting motion is small and the pressure increase may rupture the membrane.
U.S. Pat. No. 5,100,933, to Tanaka, et al., discloses the use of ionized cross-linked polyacrylamide gels as engines or artificial muscles; the gels can contain a metal ion and are capable of discontinuous volume changes induced by infinitesimal changes in environment. The gel is made by dissolving acrylamide monomers and bisacrylamide monomers in water, adding a polymerization initiator (in particular, ammonium persulfate and TEMED, or tetramethyl-ethylene-diamine) to the solution, soaking the gel sample in water to wash away all residual monomers and initiators, immersing the gel in a basic solution of TEMED for up to 60 days, then immersing the gel in a solvent (in particular, acetone, acetone in water, ethanol and water, or methanol and water). The primary disadvantages of these actuators are generally that the response time of the gel is much longer than that of other known actuator components and that the gel must be contained in the solvent bath. The gels are also mechanically brittle and easily broken.
U.S. Pat. No. 5,250,167, to Adolf, et al., discloses actuators or synthetic muscles, using polymeric gels contained in compliant containers with their solvents; these actuators undergo substantial expansion and contraction when subjected to changing environments. The actuators may be rigid or flexible and may be computer-controlled. The driver may also be electrolytic, where application of a voltage across the polymer gel causes a pH gradient to evolve between the electrodes. For example, filling the polymer fibers with platinum by alternatively treating them with solutions of platinic chloride and sodium borohydride obtains a reversible expansion and contraction of the fiber with the application of an electric field. The actuating gel itself is the only moving part required and the electric field may be only on the order of a few volts per centimeter. The disadvantage is that actuator performance is dictated by the parameters of the polymeric gel used. Furthermore, liquid containment is required to make the actuators stronger and not so easily broken.
U.S. Pat. No. 5,389,222, to Shahinpoor, discloses electrically controllable polymeric gel actuators or synthetic muscles, using gels made of polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, or polyacrylamide contained in an electrolytic solvent bath. These actuators operate by reacting to changes in the ionization of a surrounding electrolyte by expanding or contracting, and can be spring-loaded and/or mechanically biased for specific applications. Polymeric gel configurations such as sheets, solid shapes or fiber aggregates are contemplated, as are the use of a salt water solution for the electrolyte, and a platinum catalyst if) the actuator housing to recombine the hydrogen and oxygen produced as a result of electrolysis during ionization of the electrolyte. Again, liquid containment is required to maintain strength and electric controllability, and not enough deformation or displacement is generated.
Thus, there is an existing need for a soft actuator that performs activation noiselessly and efficiently (as do biological muscles) with a low ratio of mass to power or a high ratio of power or force to mass.